Combination treatment with everolimus, an inhibitor of mammalian target of rapamycin (mTOR), and exemestane (an aromatase inhibitor) is approved for use in the United States and European Union for the treatment of postmenopausal women with advanced estrogen receptor–positive (ER+)/human epidermal growth factor receptor 2–negative (HER2–) metastatic breast cancer. In this retrospective study, the patterns of treatment with everolimus and associated complications were evaluated over a 5-year period (2009-2014).

The source of these data was the MarketScan database, which is a US employment-based database that includes claim data of employees and their dependents. Breast cancer patients treated with everolimus during the 5-year evaluation period were identified, and their treatment pattern was evaluated. Additionally, the frequency of toxicities and associated emergency department visits or hospitalizations between the first claim and 30 days after the last claim for everolimus were captured.

Within this database, 2771 breast cancer patients (median age, 60 years) who received a prescription for everolimus were identified. Looking at everolimus patterns of use, the median cumulative days of supply was 112 days, with 77.2% of patients receiving an initial prescribed dose of 10 mg. The remaining patients received lower doses: 2.7% received a dose of 7.5 mg, 17.6% received 5 mg, and 2.5% received 2.5 mg. Over the course of treatment, 77.1% of patients maintained the same dose, whereas 16.9% and 6% had dose reductions or increases, respectively.

A total of 1393 (50.3%) patients in this data set had claims associated with known everolimus-related toxicities. Nausea, vomiting, and electrolyte imbalances were identified in 63.2% of patients; 34.8% had metabolic toxicities; 23.5% had hematologic toxicities; 10.7% had stomatitis; 9.4% had rash; and 0.8% had a claim for pneumonitis. Interestingly, the distribution of these toxicities differs from that reported in the everolimus clinical trials. Although these data provide real-world information on the toxicities associated with everolimus treatment, Dr Mariana Chavez-MacGregor of the University of Texas MD Anderson Cancer Center, who contributed to this study, was careful in her analysis of the results. “Cautious interpretation of our data is warranted given the limitations of claims-based research,” she said. “Toxicities related to everolimus therapy were identified, but specific causes could not be determined,” she added.